Do Cilest Contraceptive Pills Remain Effective After Their Expiry Date?

Hi, I have a packet of cilest contraceptive pills that I got given March 2014 before I went abroad for the year. I have just noticed the packet I started yesterday expired in August 2014. Should I not be taking these/ are they still effective? I am currently sexually active, so naturally I am worried about how effective they will be. Thanks!